Definition from Wiktionary, the free dictionary
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Alternative forms 
horsefly (plural horseflies)
- Any of several medium- to large flies, of the family Tabanidae, that suck the blood of mammals (not to be confused with Stomoxys calcitrans, the stable fly, or dog fly).
- (individual species or subgroups of the family Tabanidae): deer fly, yellow fly, March fly (Australia), zimb
fly of the family Tabanidae